1. Field of the Invention
The invention deals with field emission flat panel displays and with methods of forming high aspect ratio spacers to separate the anode and cathode of these displays.
2. Description of the Related Art
In field emission displays a flat anode structure is placed parallel to a flat cathode structure with a small separation distance between them A vacuum is maintained in the space between the anode structure and the cathode structure A number of spacers are typically used to maintain a uniform distance between the flat anode and the flat cathode.
The image in the field emission display is formed when electrons are emitted from a number of emitters, formed as part of the cathode structure, and impinge on a phosphor layer formed as part of the anode structure thereby forming an image. One of the problems of these displays is that the spacers used to maintain the separation between the cathode structure and the anode structure cause dark areas in the image visible to the viewer of the display. These dark areas reduce the image quality of the display. Image quality and spacers has received the attention of a number of workers in the field of displays.
U.S. Pat. No. 5,328,728 to Swirbel et al. and U.S. Pat. No. 5,389,288 to Rindo et al. teach methods of forming ball type spacers to provide spacing between parallel plates of a Liquid Crystal Display.
U.S. Pat. No. 5,379,139 to Sato et al. shows the use of photoresist pillars as spacers for Liquid Crystal Displays but does not teach how the pillars are formed.
U.S. Pat. No. 5,338,240 to Kim teaches the use of elongated spacers for a Liquid Crystal Display. U.S. Pat. No. 4,975,104 to Kim teaches a method of forming barrier ribs to provide separation in a gas display panel.
U.S. Pat. No. 5,232,549 to Cathey et al. teaches forming spacers for flat panel displays by forming a layer of polymer material from which the spacers will be formed. A pattern of reflective material is formed on the polymer and the unwanted polymer material is removed with a laser. Alternately a laser is used to form holes in an etchable material. The holes are filled with spacer material and the etchable material is etched away.
U.S. Pat. No. 5,385,499 to Ogawa et al. teach a method of forming spacers by coating glass balls with glass frit of a low softening point. The assembly is heated and the glass frit is coalesced to form a sheath around the glass balls and a bond with wettable areas on the substrate. The excess glass balls are then removed and the remaining glass balls form spacers.